This invention relates to an osmotic pressure sensing head.
The measurement of the osmotic pressure of blood protein molecules in the blood, has become important in the diagnosis of edema, and especially pulmonary edema. It is believed that fluid moving into the alveoli of the lung, which prevents oxygenation of the blood, is due to low levels of blood proteins whose osmotic pressure would normally draw fluid from the alveoli into the capillaries. The plasma colloid osmotic pressure, often referred to as the oncotic pressure, can be measured in a sensing head which includes a reference chamber containing saline solution, a sample chamber for receiving blood plasma, and an osmotic membrane between the chambers which allows saline (NaCl) molecules to pass through while preventing the passage of the much larger protein molecules of the blood. A pressure transducer coupled to the reference chamber measures the pressure resulting from the osmotic pressure of the blood proteins to thereby indicate the concentration of the blood proteins. While such a sensing head enables more rapid determination of the concentration of blood proteins than can be achieved by centrifuging of the proteins and weighing them, the maintenance and operation of such a sensing head is a delicate and often difficult task. The sensing head is normally stored with saline solution on both sides to preserve the membrane. The stored saline solution must be removed and replaced by the blood plasma before each measurement, and the blood plasma must be fully removed after each measurement and the membrane cleaned. Actually, whole blood can be utilized, provided that precautions are taken to adequately clean the membrane of any blood components. However, membrane cleaning by blotting or by use of vacuum devices to remove residue is a difficult procedure, inasmuch as the membrane can be easily damaged.